SOLAR SYSTEM

Detailed explanation-1: -Class I: a class for the blue/white stars that exhibited strong, broad hydrogen lines. Class II: yellow stars with weaker hydrogen features, but with evidence of rich, metallic lines. Class III: red stars with complex spectra, with huge sets of absorption features.

Detailed explanation-2: -In 1866, Angelo Secchi, a Jesuit astronomer working at the Vatican Observatory, surveyed some 4, 000 stars and classified them by the visual appearance of their spectra. He divided stars into four broad, numbered categories based on common spectral features.